1. Field of the Invention
The present invention relates to a sewing machine, more particularly to a sewing machine having a presser foot for preventing cloth from lifting up when the needle is pulled out of the cloth, which presser foot is adapted to move up and down synchronizing with the up-and-down movement of the needle bar.
2. Description of the Prior Art
As shown in FIG. 12A, a holding frame 11f provided above a bed 3f is installed with a needle bar 6f for moving up and down which has a driven piece 16f to receive a driving force from a needle bar lifting mechanism 8f and a sewing needle 15f. The needle bar 6f is attached with a presser foot holder 20f for relatively moving up and down which has a presser foot 29f attached at its lower end for preventing cloth 65f from lifting up when the needle 15f is pulled out of the cloth 65f and which holder 20f is energized downward by a spring 31f. On the other hand, a retainer 47f is provided for moving up and down along the presser foot holder for controlling the up-and-down movement of the presser foot holder 20f by supporting it upward. The retainer 47f is provided with a cushion piece 48f on its upper surface, and is linked to a driving mechanism 49f for driving the retainer 47f to reciprocate up and down synchronizing with the up-and-down movement of the needle bar 6f. The presser foot holder 20f is secured with a guide member 23f at its upper end, which is provided with an engaging portion 28f for engaging with the retainer 47f. Moreover, a needle chuck 14f provided at the lower end of the needle bar serves as a lifting member for lifting a contact member 24f at the lower end of the presser foot holder 20f as the needle bar 6f moves upward.
The above-described arrangement operates as follows. When the needle bar 6f is caused to move downward by the needle bar lifting mechanism 8f, the presser foot holder 20f is caused to move downward through the spring 31f, and the engaging portion 28f is brought into contact with the retainer 47f as shown in FIG. 12B. Thereafter, the retainer 47f is caused to move downward by the driving mechanism 49f synchronizing with the downward movement of the needle bar 6f. When the lower end of the presser foot 29f reaches to the position just prior to contact with the bed 3f as shown in FIG. 12C, the downward movement of the retainer 47f is stopped, so that the presser foot 29f is retained at that position. In the meantime the needle bar 6f moves further downward to become the condition as shown in FIG. 12D. Then, in the process where the needle bar 6f moves upward from the condition as shown in FIG. 12D and the needle 15f is pulled out of the cloth 65f, the presser foot 29 prevents the cloth 65f from lifting up. Then, the lifting member 14f abuts against with the contact member 24f as shown in FIG. 12C. Thereafter, as shown in FIG. 12B, the presser foot holder 20f is lifted by the needle bar 6f and simultaneously the retainer 47f is also moved upward together by the driving mechanism 49f. And, as shown in FIG. 12A, when the needle bar 6f moves upward to its upper limit, the presser foot holder 20f is lifted up, through the engagement of the lifting member 14f and contact member 24f, to its upper limit higher than the range of the up-and-down movement by the retainer 47f, so that a clearance Gf is made between the retainer 47f and the engaging portion 28f (for instance, see the Kokal tokkyo koho No.5-245278).
According to the above-described arrangement, the presser foot 29f can prevent the cloth 65f from lifting up when the needle 15f is pulled out of the cloth 65f, so that smooth sewing is made possible. Moreover, when the needle bar 6f has been lifted up, the presser foot 29f also can be lifted up to a position above the bed 3f, so that it is made possible to traverse the cloth 65f freely on the bed 3f and the sewing work of free design is made possible. Besides, the downward movement of the presser foot 29f is made to stop at the position where the presser foot 29f does not abut against the bed 3f, so that the cloth 65f can be prevented from damage by pressing it to the bed 3f.
Moreover, when the needle bar 6f has been lifted up as shown in FIG. 12A, a clearance Gf can be formed between the retainer 47f and the engaging portion 28f, so that in a multi-needle sewing machine (for instance, a multi-needle sewing machine relating to one head of a multi-head sewing machine as known in U.S. Pat. No. 4,531,467), exchange of one needle bar 6f of the multineedle bars to another one is made possible by the lateral movement of the holding frame 11f. Furthermore, when the engaging portion 28f abuts against the retainer 47f in spite of the existence of the the clearance Gf as the presser foot holder 20f moves downward, the retainer 47f can be left previously to start in to move downward slowly by the driving mechanism 49f, so that the difference of the speed between the engaging portion 28f and the retainer 47f is made small and the sound of collision of them can be made small.
Also, even when there is a few difference of speed between the engaging portion 28f and retainer 47f, collision of them can be absorbed by the cushion piece 48f, so that the sound of collision can be made small. In this conventional sewing machine the cushion piece 48f plays an important role. But, if the cushion piece 48f is left out during the working of the sewing machine as shown in FIG. 12E, the presser foot 29f in the downward moving reaches to the lower position, in spite of stopping of the retainer 47f, by the thickness of the cushion piece 48f in comparison with the normal condition where the cushion piece 48f exists in place, and it results in the collision of the lower end of the presser foot 29f with the bed 3f. Then, the presser foot 29f repeatedly collides with the bed due to the high speed operation of the sewing machine, so that the generated big sound surprises the operator, the presser foot 29f is damaged, or the cloth 65f on the bed 3f is damaged. Difficulty in continuing the sewing work results.